A hard-disk drive (HDD) positions a head-slider by servo control using servo patterns on a magnetic-recording disk and writes, or alternatively, reads, data at an address designated by a host. An operation for writing servo patterns to magnetic-recording disks is called servo writing; and, servo writing is generally performed in the manufacturing of HDDs. As one type of a servo write operation, self-servo writing (SSW) is known in the art; SSW reads out data written by the HDD for head-slider positioning and timing control to write servo patterns to magnetic-recording disks.
For writing new servo patterns to a magnetic-recording disk in SSW, a HDD writes servo patterns for head-slider positioning and timing patterns for measuring the timing of writing new servo patterns. The servo patterns written by the HDD typically include two types of servo patterns: servo patterns used in read and write operations corresponding to commands from a host, which are referred to herein by the term of art “product servo patterns” that are further described herein, and servo patterns used only for the servo control in SSW. As described herein, servo patterns are patterns for head-slider positioning, which is associated with actuator positional control, including both types of servo patterns.
SSW performs timing control by timing patterns to write new servo tracks while reading out servo patterns written by the HDD itself for head-slider positioning, which is associated with actuator positional control. The HDD repeats such a propagation process of servo patterns. A read element and a write element on a head-slider are located at different radial positions of the magnetic-recording disk and the read element can read servo patterns written by the write element. Typically, the read element is located closer to an inside diameter (ID) of the magnetic-recording disk than the write element, and the read element reads servo patterns written by the write element and the write element writes a new servo track closer to an outside diameter (OD) of the magnetic-recording disk.
The clearance between a magnetic-recording disk and a magnetic-recording head, which includes a read element and a write element, flying in proximity to the recording surface of the magnetic-recording disk is reduced; and, variations in the clearance are also reduced to increase the recording density of the magnetic-recording disk. To this end, some mechanisms to adjust the clearance have been proposed. One of these mechanisms employs a heater in a magnetic-recording head and adjusts the clearance by heating the magnetic-recording head with the heater. As used herein, this mechanism is referred to by the term of art, “thermal fly-height control” (TFC). TFC supplies the heater with current to liberate heat and protrudes the magnetic-recording head by thermal expansion. TFC reduces the clearance between the magnetic-recording disk and the magnetic-recording head. In addition, another mechanism is known in the art to adjust the clearance between the magnetic-recording disk and the magnetic-recording head with a piezoelectric element.
Engineers and scientists engaged in HDD manufacturing and development are interested in servo writing methodologies and systems utilized by HDDs that can increase the recording density of information stored on a magnetic-recording disk, to meet the demands of the marketplace for performance and reliability of HDDs.